1. Field of the Invention
The present invention relates to a hydraulic control device for an automatic transmission mounted in a vehicle or the like, and particularly to a hydraulic control device for an automatic transmission by which oil is supplied into or discharged from a starting device having a hydraulic power transmission and a clutch that can lock up the hydraulic power transmission, oil is fed out to an oil cooler to cool the oil, and oil is supplied into an automatic transmission mechanism to lubricate the automatic transmission mechanism.
2. Description of the Related Art
An automatic transmission mounted in a vehicle or the like is equipped with a starter for transmitting the output of a driving source to the input shaft of a transmission mechanism, that is, the starter is provided with a torque converter that can permit the difference in rotational number between the output shaft (crank shaft) of an engine and the input shaft of the transmission mechanism by performing hydraulic power transmission. Furthermore, some starters of automatic transmissions as described above are equipped with lockup clutches that can set (lock up) the output shaft of the engine and the input shaft of the transmission mechanism to a direct coupling state to improve fuel-efficiency or the like.
In general, a hydraulic circuit of an automatic transmission having a torque converter as described above is constructed so that oil discharged from the starter is supplied to an oil cooler to cool oil whose temperature is increased in the torque converter when the lockup clutch is released, and also constructed so that oil is supplied through the oil cooler into a lubricant path of the transmission mechanism to improve the cooling property of the respective parts of the transmission mechanism (for example, see JP-A-8-135772 (Patent Document 1)).
There is a case where minute foreign materials occur in the torque converter of the automatic transmission when it is manufactured, and thus a step of removing these foreign materials is provided in the manufacturing process. However, the foreign materials cannot be perfectly removed even when the process is passed through the foreign material removing step. Accordingly, when the lubricant path is constructed in series with the torque converter as in the case of the Patent Document 1, these foreign materials invade into the lubricant path, which causes abrasion of the respective parts of the transmission mechanism.
Furthermore, with respect to the hydraulic circuit in which the torque converter, the oil cooler and the lubricant path are arranged in series as in the case of the Patent Document 1, for example under a low oil temperature state immediately after the engine is started or the like, the viscosity of the oil is high and the duct resistance is large. Accordingly, there is a problem that the lubricant to be supplied to the respective parts of the transmission mechanism runs short, supply of oil into an oil chamber for canceling centrifugal hydraulic pressure of the clutch arranged in the transmission mechanism is delayed or the like.